Looking Up: First quarter & half a moon

Peter Becker More Content Now

Friday

Aug 17, 2018 at 11:48 AMAug 17, 2018 at 11:48 AM

Q. When does the Man of the Moon most resemble George Washington?A. At "quarter" phase.

The moon reaches first quarter on Saturday, August 18. This week, watch as the moon puffs out, in its waxing gibbous phase heading for fullness on August 26.I can’t remember my first quarter though it probably was from the tooth fairy. Hopefully I even earned a quarter sometime along the way as a kid. I’ll never tell!

The moon at first quarter can be likened to the capital letter "D," a half circle, with its straight side on the left. This assumes you’re looking from the northern hemisphere. It may be strange to visualize but below the equator, the moon’s orientation as well as the constellations, are flipped right over!

I have pondered why they don’t call it a "half moon" since half the moon is shining, not just a quarter. The "quarter" part means that the moon has moved one quarter the way around in its monthly orbit about the Earth.

If you have even a small telescope, or good binoculars on a steady tripod or other support, this is an excellent time to see the lunar craters and mountainous areas. The boundary between the lit part of the Moon and the dark side is known as the terminator, and the sunlight casts shadows in and around the carters and behind each lunar mountain. This makes the lunar surface seem to stand out in bold relief.

You can watch the ever changing array of the terminator as the moon moves through its phases from crescent to quarter to gibbous, revealing whole new areas in stunning detail.

Earthshine, the dim glow of the darkened portion of the moon caused by Earth’s reflection, can still be seen at quarter phase if you look with a telescope and keep the bright portion out of your eyepiece field of view.

First quarter moon sets around midnight (1 a.m. daylight savings time). Depending on your latitude and time of the year, the moon’s orientation as it approaches the horizon makes it look like an upright cereal bowl seen from the side.

Full moon presents its face in glaring sunshine, and appears washed out. Yet, the full moon has a beauty all its own and reveals other aspects of the interplay of light and dark across the moon. Rays from certain craters such as Tycho spread across the lunar face, and are best seen when the moon is full or almost so.

After full moon you can watch the whole changing display in reverse as the moon goes through its waning phases on the way past last quarter to new moon.

Interestingly, more than half the moon is visible to us; in fact, 59 percent of the moon can be seen from Earth, but not at the same time. What is referred to as libration, the moon nods slightly as it moves in its orbit, providing a peek around to the far side.

Only 27 men have ever seen the far side: the Apollo astronauts who orbited the moon on nine missions between 1968 and 1972 (seven were landing missions). Perhaps in not so many years astronauts will see it again.

Why do we only see one side? Locked in a gravitational balance, the moon rotates once for every time it goes around the Earth, always keeping the same time facing the planet. This is called "synchronous rotation."

It’s incorrect to refer to the far side of the moon as the "dark side" unless you mean when the moon is in full phase. Only at that time is the "back" of the moon fully away from the sunlight.

Enjoy the passage of the moon, Earth’s familiar and constant companion, and like a friend to Earth’s inhabitants who have seen it all their lives with childlike wonder.

Keep looking up!

— Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at news@neagle.com. Please mention in what newspaper or web site you read this column.

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